Run Xiong

Transient Resistance Analysis of Large Grounding Systems Using the FDTD Method

In this work, a new method has been proposed for the flnite-difierence time-domain (FDTD) analysis of the transient grounding resistance (TGR) of large grounding systems. To calculate the TGR, a coarse grid is occupied to model the earthing conductor, the convolution PML (CPML) is chose to truncate the computational domain, and the parallel implementation is involved to overcome the memory limit of the serial FDTD. With this model, the efiect of the earthing conductor number and topology structure, the buried depth, and the ground permittivity and conductivity on the TGR is tested to flnd an optimized program to decrease the TGR of the lightning protection grounding systems.

A numerically efficient method for the FDTD analysis of the shielding effectiveness of large shielding enclosures with thin-slots

A numerically efficient method for the finite-difference time-domain (FDTD) analysis of shielding effectiveness (SE) of large shielding enclosures has been proposed in this paper. FDTD has been widely applied in the SE analysis, but it is difficult to analyze the SE using the standard FDTD method when large shielding enclosures with thin-slots are involved. To model the narrow apertures without involving too much memory occupation, the thin-slot formalism is adopted. The parallel implementation is induced into the simulation in order to overcome the limitation of a single processors memory. To decrease the simulating time, windowing technique is used in the SE analysis. By using these artifices, the FDTD analysis of large shielding enclosures can be carried out efficiently.

FDTD Modeling of the Earthing Conductor in the Transient Grounding Resistance Analysis

The grounding system plays an important part in the lightning protection system of power and communication systems. The finite-difference time-domain (FDTD) method is widely used in modeling complex electromagnetic interaction problems. However, it is difficult to model the earthing conductor using the standard FDTD method in the transient grounding resistance (TGR) analysis for the electrically small depth of the earthing conductors. In this letter, a new method has been proposed to model the earthing conductor by incorporating the singularities of the field variation near the conductor into the Faradays contour path. The efficiency of the proposed model has been approved by verifying both the supposed field distribution near the earthing conductor and the TGR.

Improved Formalism for the FDTD Analysis of Thin-Slot Penetration by Equivalence Principle

An improved formalism by the equivalence principle has been verified to be an accurate model of the field distribution near a thin slot for the finite-difference time-domain analysis of the thin-slot penetration.

An Algorithm for the FDTD Modeling of Flat Electrodes in Grounding Systems

A sub-cell algorithm for the finite-difference time-domain (FDTD) modeling of flat electrode in grounding systems is proposed. The electromagnetic field variation near a flat electrode is derived from the integral of the differential electric field which is radiated by the distributed charge on an electrostatic charged flat electrode. By fully incasing the field singularity into the coarse cells containing the electrode with the Faradays Law, a sub-cell algorithm has been proposed to reduce computational resources when modeling the flat electrode. The accuracy of the derived field singularity is verified from comparison with the field given by the high-resolution standard FDTD simulation. The efficiency of the proposed algorithm has been approved by verifying the transient grounding resistance (TGR) of the grounding system using the proposed algorithm and the computational memory and time usage.

Optimized Programs for Shaped Conductive Backfill Material of Grounding Systems Based on the FDTD Simulations

A new transient grounding resistance calculation model is proposed for the finite-difference time-domain (FDTD) method. In FDTD, the perfectly matched layer is backed by the perfect electric conductor (PEC) wall. By stretching the grounding system lifting line to the PEC wall, the grounding system performance is simulated. With this model, a 2-D cylindrical coordinate domain FDTD simulation was carried out to study cylindrically shaped conductive backfill material (SCBM) performance with fine grids. From experimental results, some optimal programs have been derived for SCBM in grounding systems. It is found that a large metal rod size can reduce the SCBM resistance only when the main body conductivity is low, and the reduction effect declines as the conductivity increases. Second, the SCBM resistance is as low as the resistance of a conductor of the same size when the main body conductivity reaches 0.5 S/m. Third, enlarging the SCBM radius can reduce the grounding resistance, and resistance can also be reduced by enlarging the SCBM length when it is less than its effective length. Fourth, the grounding resistance of an SCBM, whose conductivity is linear or parabolic type varied, can be as low as that of a totally high conductivity SCBM.

An Unconditionally Stable One-Step Leapfrog ADI-BOR-FDTD Method

In this letter, an unconditionally stable one-step leapfrog alternating-direction-implicit finite-difference time-domain (ADI-FDTD) method for body of revolution (BOR) is proposed. It is more computationally efficient while preserving the properties of the original alternating-direction-implicit body of revolution finite-difference time-domain (ADI-BOR-FDTD) method. Due to the singularity, some field components on and adjacent to the axis are treated especially. To verify the accuracy and efficiency of the method, the scattered field from a PEC cylinder with a notch is calculated.

The Capacitance Thin-slot Formalism Revisited: An Alternative Expression for the Thin-Slot Penetration

The capacitance thin-slot formalism is investigated, in which the effective permittivity is found to be time varying while the effective permeability is nearly constant. Additionally, it is found that the effective permeability is not equal to the reciprocal of the effective permittivity. Based on the improved formalism of the field distributions and numerical results, an alternative expression is derived for the thin-slot penetration by modifying coefficients of the updating equations near the slot. High-resolution standard finite difference time domain method (FDTD) result and commercially available numerical tool FEKO result are presented in support of the new expression.

A unified radiative magnetohydrodynamics code for lightning-like discharge simulations

A two-dimensional Eulerian finite difference code is developed for solving the non-ideal magnetohydrodynamic (MHD) equations including the effects of self-consistent magnetic field, thermal conduction, resistivity, gravity, and radiation transfer, which when combined with specified pulse current models and plasma equations of state, can be used as a unified lightning return stroke solver. The differential equations are written in the covariant form in the cylindrical geometry and kept in the conservative form which enables some high-accuracy shock capturing schemes to be equipped in the lightning channel configuration naturally. In this code, the 5-order weighted essentially non-oscillatory scheme combined with Lax-Friedrichs flux splitting method is introduced for computing the convection terms of the MHD equations. The 3-order total variation diminishing Runge-Kutta integral operator is also equipped to keep the time-space accuracy of consistency. The numerical algorithms for non-ideal terms, e.g., arti...

A Novel Weakly Conditionally Stable FDTD Method for Periodic Structures

In this letter, a novel weakly conditionally stable finite-difference time-domain (FDTD) method for solving periodic structures is presented, which is extremely useful for periodic problem with thin slots in one or two directions. To verify the validity of the proposed formulations, a numerical example of electromagnetic band-gap (EBG) structure with thin slots is given. Compared to the alternating-direction implicit FDTD (ADI-FDTD) method, the presented method has higher accuracy and efficiency. Results show the running time can be reduced to about 2/3 of the periodic ADI-FDTD method in the same simulation. To reduce the numerical dispersion error, the optimized procedure is applied.